A conventional communication system for a vehicle is capable of executing various kinds of remote control carried out from a location outside a vehicle. Typically, the control is executed to lock and unlock doors of the vehicle, open and retract door mirrors of the vehicle, open and close power windows of the vehicle, open and close slide and back doors of the vehicle as well as start and stop the engine of the vehicle.
This communication system comprises a portable transmitting apparatus, which has a plurality of operation switches, and a receiving apparatus mounted on the vehicle. When a user carrying the transmitting apparatus operates a predetermined operation switch, the transmitting apparatus transmits operation information corresponding to the operated operation switch as a radio wave. The operation information indicates the type of the operated operation switch. Receiving the radio wave, the receiving apparatus mounted on the vehicle supplies the operation information conveyed by the radio wave to a control apparatus employed in the vehicle.
In a typical configuration of the communication system of this type, the transmitting apparatus transmits operation information as a radio wave only if the user operates an operation switch provided on the transmitting apparatus. To have the transmitted radio wave reach the receiving apparatus mounted on a vehicle with a high degree of reliability, the user must operate the operation switch at a location sufficiently close to the vehicle. Therefore, the communication system cannot be used with a high degree of convenience.
For this reason, a communication system disclosed in JP-A-2001-355363 is proposed. In this proposed communication system, if the user operates an operation switch, the transmitting apparatus thereafter continues transmission of operation information for a predetermined period of time even if the user stops the operation carried out on the operation switch. In the proposed communication system, however, the time of the transmission of operation information corresponding to an operation switch operated by the user is merely extended. Thus, the content of a command cannot be expressed in terms of the number of switch operations or the operation duration.
In the communication system for remotely controlling a vehicle as described above, with an increasing number of control types each executed as a command issued by a remote control, the user becomes most likely prone to misoperations carried out on operation switches inadvertently as the operations causing incorrect control. Thus, if the number of control types each executed as a command issued by a remote control becomes greater than that of the conventional communication system, the content of a command needs to be expressed not only in terms of the type of an operation switch, but also in terms of the number of switch operations and the operation duration.
In the proposed communication system, however, once an operation switch is operated, the transmitting apparatus thereafter merely continues transmission of operation information for a predetermined period of time. Thus, even through the content of a command can be expressed in terms the type of an operation switch, it cannot be expressed in terms of the number of switch operations and the operation duration.
In addition, to convey the content of a command given to a control apparatus employed in a vehicle not only in terms of the type of an operation switch, but also in terms of the number of switch operations and the operation duration, it is necessary to design the transmitting apparatus into such a configuration that the transmitting apparatus transmits operation information corresponding to an operation switch only if the user operates the operation switch.
In the case of a transmitting apparatus with such a configuration, if only operation information indicating the type of an operated operation switch is transmitted as a radio wave as is the case with the conventional communication system, however, the user must operate the operation switch at a location sufficiently close to a vehicle to have the radio wave transmitted by the transmitting apparatus reach the receiving apparatus mounted on the vehicle with a high degree of reliability. Therefore, the transmitting apparatus with such a configuration cannot be used with a high degree of convenience.